/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.hadoop.hbase.client;

import java.io.IOException;
import java.util.Iterator;

/**
 * Helper class for custom client scanners.
 */
public abstract class AbstractClientScanner implements ResultScanner {

	@Override
	public Iterator<Result> iterator() {
		return new Iterator<Result>() {
			// The next RowResult, possibly pre-read
			Result next = null;

			// return true if there is another item pending, false if there isn't.
			// this method is where the actual advancing takes place, but you need
			// to call next() to consume it. hasNext() will only advance if there
			// isn't a pending next().
			public boolean hasNext() {
				if (next == null) {
					try {
						next = AbstractClientScanner.this.next();
						return next != null;
					} catch (IOException e) {
						throw new RuntimeException(e);
					}
				}
				return true;
			}

			// get the pending next item and advance the iterator. returns null if
			// there is no next item.
			public Result next() {
				// since hasNext() does the real advancing, we call this to determine
				// if there is a next before proceeding.
				if (!hasNext()) {
					return null;
				}

				// if we get to here, then hasNext() has given us an item to return.
				// we want to return the item and then null out the next pointer, so
				// we use a temporary variable.
				Result temp = next;
				next = null;
				return temp;
			}

			public void remove() {
				throw new UnsupportedOperationException();
			}
		};
	}
}
